1. Field of the Invention
The present invention relates to a method of driving a plasma display panel having a plurality of scan electrodes aligned in a row direction, a plurality of data electrodes aligned in a column direction, and a plurality of sustain electrodes that are formed parallel with the scan electrodes and that are each paired with a scan electrode.
2. Description of the Related Art
As flat display panels that can be readily applied to large-screen applications, plasma display panels (hereinbelow abbreviated xe2x80x9cPDPxe2x80x9d) that can be used for such purposes as a display output of personal computers, display output of work stations, and wall-hung televisions can be divided between two types depending on the operating method. One type is the direct-current discharge PDP in which electrodes are exposed to discharge gas and discharge is brought about only during the application of voltage, and the other is alternating-current PDP in which electrodes are covered with a dielectric and discharge is brought about without exposing the electrodes to discharge gas. The alternating-current PDP (hereinbelow referred to as xe2x80x9cAC-PDPxe2x80x9d) has a memory capability in the discharge cells themselves due to the charge-storing effect of a dielectric.
FIG. 1 is a section view showing the configuration of a typical AC-PDP of the prior art. In the AC-PDP shown in FIG. 1, the construction described hereinbelow is formed in a space enclosed between front substrate 10 containing glass and rear substrate 11 similarly containing glass.
Scan electrodes 12 and sustain electrodes 13 are alternately formed at a prescribed spacing on front substrate 10. Scan electrodes 12 and sustain electrodes 13 are covered with insulation layer 15a, and protective layer 16 that protects insulation layer 15a from discharge and contains, for example, MgO, is formed on insulation layer 15a. In addition, data electrodes 19 are formed on rear substrate 11 orthogonal to scan electrodes 12 and sustain electrodes 13 on front substrate 10. Data electrodes 19 are covered with insulation layer 15b, and phosphor 18 is applied on insulation layer 15b to effect display by converting ultraviolet rays generated by discharge into visible light. In addition, barrier ribs 17 that both establish discharge spaces 20 and demarcate pixels are formed between insulation layer 15a on front substrate 10 and insulation layer 15b on rear substrate 11. A gas mixture of, for example, helium, neon and xenon is charged within discharge spaces 20 as the discharge gas.
FIG. 2 is a plan view showing the arrangement of electrodes in the AC-PDP shown in FIG. 1. In the electrode configuration of the AC-PDP shown in FIG. 2, m scan electrodes 12i (i=1, 2, . . . , m) are formed in the row direction, n data electrodes l9j (j=1, 2, . . . , n) are formed in the column direction, one pixel being formed at each point of intersection. Sustain electrodes 13i are formed in the horizontal direction to form pairs with scan electrodes 12i, scan electrodes 12i and sustain electrodes 13i being mutually parallel. A color display AC-PDP is produced by separately applying phosphor 18 shown in FIG. 1 to each pixel in the three colors Red, Green, and Blue.
FIG. 3 is a timing chart showing the waveforms of the drive voltage applied to each electrode of the AC-PDP shown in FIG. 2. Explanation is next presented regarding the drive method of an AC-PDP of the prior art with reference to FIG. 3.
Extinguishing pulse 21 is first applied to all scan electrodes 12 to extinguish pixels that were emitting light before the time shown in FIG. 3, whereby all pixels are extinguished. Next, preparatory discharge is effected by applying preparatory discharge pulse 22 to sustain electrodes 13 to force all pixels to discharge and emit light. Preparatory discharge extinguishing pulse 23 is then applied to scan electrodes 12 to extinguish the preparatory discharge of all pixels. This preparatory discharge facilitates subsequent write discharge.
After extinguishing the preparatory discharge, scan pulses 24 are applied to each of scan electrodes 121-12m at a staggered timing, and, synchronized to the timing of the applied scan pulses 24, data pulses 27 that correspond to display data are applied to data electrodes 191-19n. The diagonal lines of data pulses 27 in FIG. 3 indicate that the presence or absence of data pulses 27 is determined according to the presence or absence of display data. Write discharge occurs within discharge spaces 20 between scan electrodes 12 and data electrodes 19 shown in FIG. 1 in pixels in which data pulse 27 is applied at the time of scan pulse 24 is applied, and write discharge does not occur if data pulse 27 is not applied at the time scan pulse 24 is applied.
In a pixel in which write discharge occurs, a positive charge referred to as a wall charge is stored in insulation layer 15a at scan electrode 12. At this time, a negative wall charge is stored on insulation layer 15b on data electrode 19. First sustain discharge occurs due to the combination of the positive potential due to the positive wall charge formed on insulation layer 15a on scan electrodes 12 and first sustain discharge pulse 25 of negative polarity that is applied to sustain electrodes 13. When first sustain discharge occurs, a positive wall charge is stored in insulation layer 15a at sustain electrode 13 and a negative wall charge is stored in insulation layer 15a over scan electrode 12, thereby forming a potential difference. The potential difference due to these wall charges combines with second sustain discharge pulse 26 applied to scan electrodes 12, generating a second sustain discharge. Sustain discharge thus continues with the potential difference caused by wall charge formed by the xth sustain discharge combining with the (x+1)th sustain discharge pulse. The amount of emitted light is controlled by the number of times sustain discharge is continued.
If the voltages of sustain discharge pulse 25 and sustain discharge pulse 26 are adjusted in advance to a level such that discharge is not generated by these pulse voltages alone, first sustain discharge will not occur despite the application of first sustain discharge pulse 25 in pixels in which write discharge has not occurred because there is no potential due to wall charge before first sustain discharge pulse 25 is applied, and subsequent sustain discharges will also not occur.
Sustain discharge pulse 25 and sustain discharge pulse 26 are usually applied to sustain electrodes 13 and scan electrodes 12 at a frequency on the order of 100 kHz. In addition, sustain discharge pulse 25 and sustain discharge pulse 26 have phases shifted 180xc2x0 to each other. The frequency of generation of sustain discharges is on the order of 200 kHz because sustain discharge pulses 25 are alternately applied to sustain electrodes 13 and scan electrodes 12.
Explanation is next presented regarding the gray-scale display method of an AC-PDP. In an AC-PDP, the drive sequence explained in FIG. 3 is referred to as a sub-field. Essentially, the display ON/OFF is determined by write discharge in a sub-field, and the luminance of the emitted light is determined by the number of times of sustain discharge.
FIG. 4 is a chart showing the rate of the number of sustain discharge pulses during one image display period. Gray-scale display by sub-field divisions is explained with reference to FIG. 4. Referring to FIG. 4, in an usual AC-PDP, one image display period is divided into a plurality of subfields, and ON/OFF control of display is effected in each sub-field. If the number of sustain discharges varies in each sub-field and, for example, the ratio of the number of sustain discharges is made 1:2:4:8 in a four sub-field division, 16 tones can be displayed by means of the ON/OFF control of each sub-field. In other words, tones in 16 gradations can be displayed from a gray-scale level of 0 when the display of all sub-fields is OFF up to a gray-scale level of 15 when the display of all sub-fields is ON.
In a color PDP of the prior art, the number of sustain discharges must be increased to increase the luminance of emitted light. Accordingly, either of two measures are adopted to increase the luminance of emitted light, one being a method in which the drive frequency is raised without changing the sustain discharge period, and the other method being a method in which the sustain discharge period is lengthened while increasing the number of sustain discharge pulses. In either of the measures, however, there are the problems that the.luminous efficiency decreases with the occurrence of both saturation of ultraviolet light emission caused by sustain discharge and the saturation of the fluorescent emission that is excited by the ultraviolet light, and increase in the luminance of emitted light incurs a disproportionately greater increase in power consumption.
It is an object of the present invention to provide a PDP drive method that enables high luminance of emitted light at low power consumption and without a decrease in luminous efficiency when carrying out sustain discharge.
To achieve the above-described object, the present invention divides a sustain discharge period of at least one sub-field from a plurality of sub-fields into a plurality of sub-sustain discharge periods; sets a first sustain discharge frequency as the sustain discharge frequency of an initial first sub-sustain discharge period of these sub-sustain discharge periods; and sets a second sustain discharge frequency that is lower than the first sustain discharge frequency as the sustain discharge frequency of the second final sub-sustain discharge period of the sub-sustain discharge periods.
Alternatively, the sustain discharge period of at least one sub-field of the plurality of sub-fields is divided into a plurality of sub-sustain discharge periods; and first sub-sustain discharge periods in which sustain discharge is effected and second sub-sustain discharge periods in which sustain discharge is not effected are arranged alternately.
As yet another alternative, a third drive frequency of a third sustain discharge pulse, which is at least one of the first drive frequency of the first sustain discharge pulse applied to the scan electrodes and the second drive frequency of the second sustain discharge pulse applied to the sustain electrodes, is varied within the sustain discharge period.
In other words, the present invention sets the sustain discharge frequency of at least one of the sustain electrodes and scan electrodes to a high frequency during the first half of a sustain discharge period in which the number of discharges is low and the effect of light saturation is insignificant, and, in order to lessen the effect of light saturation, sets the sustain discharge frequency of at least one of the sustain electrodes and scan electrodes to a low frequency during the second half of a sustain discharge period in which the number of discharges has become high and the effect of light saturation must be taken into consideration. In addition, a blank period of at least one sustain discharge pulse of the sustain electrodes and scan electrodes is provided during a sustain discharge period before the number of sustain discharges becomes great and the light saturation is reached, following which sustain discharge is again carried out. As a result, the light saturation phenomenon can be suppressed even though the number of sustain discharges becomes great, and high luminance can be obtained with low power consumption and without a drop in luminous efficiency.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.